The present invention relates to a passenger restraining protective device and, more specifically, to a passenger restraining protective device that determines the state of the younger passenger sitting on a child seat fixed on the seat or on a booster seat and regulates the actuation of the air bag according to the circumstances.
In vehicles provided with an air bag as a passenger restraining protective device for the front passenger seat, the air bag is inflated and deployed upon collision to protect an adult passenger sitting on the front passenger seat from the secondary collision in the car. On the other hand, in case where a baby or infant seat, a child or toddler seat, or a booster seat is mounted on the front passenger seat and an infant or the like is using the front passenger seat, there may be a case where complete deployment of the air bag is not desirable for safety reasons. Therefore, realization of the system that determines the case where an infant or a child with the stature smaller than that for an average six year old child (for example) is sitting on the front passenger seat and, accordingly, decreases a force to deploy the air bag or prohibits the deployment itself is required.
Conventionally, there is a circuit that determines whether or not a passenger is sitting on the seat to serve as an alarm for reminding the passenger to fasten the seat belt. In this determination circuit, a seat sensor determines the weight applied on the seat and turns an alarm lamp on the instrument panel ON when the seat belt is not fastened yet.
The seat sensor is a known weight sensor mounted at the bearing position on the floor of the car body where the leg section of the seat is fixed. By performing a calibration of an empty weight in advance, the weight of the passenger seated on the seat or the baggage placed on the seat may be detected as a value of the load (hereinafter the load is referred to as a seat weight). On the other hand, whether or not the seat belt is appropriately fastened may be checked by the ON-state of the known buckle switch.
For example, the following circumstances may be considered as typical cases where the air bag should not be deployed. FIG. 8 is an explanatory drawing illustrating the state of the passenger in each case in a schematic manner connect. Case 1 shows a baby seat 51 is fixed on the seat 50 facing toward the rear with a seat belt 52, and a baby is lying thereon. Case 2 shows where a child seat 55 is fixed on the seat 50 with the seat belt 52 and an infant (approximately up to 4 years old) 56 is sitting thereon. Case 3 shows a booster seat 58 is placed on the seat 50 and an infant (approximately up to 6 years old) 57 is sitting thereon with the seat belt 52 fastened. It is desirable to deploy the air bag 60 when an elementary school age child of a fourth grade or higher/or a small-statured adult (approximately 48 kg in weight) 59 is sitting on the seat with the seat belt 52 fastened (Case 4). Therefore, in order to discriminate Cases 1 to 3 and Case 4, the seat weight obtained by the seat sensor 70 (See FIG. 6) is used a basic variable. The average values of the seat weight are shown in the upper column of the Table 1 (when the seat belt is not yet fastened).
As shown in Case 2, the child seat is fastened on the seat with a seat belt, and one end of the lap belt of the seat belt is anchored to the floor of the car body. In the seat having such a structure, a belt tension generated when the seat belt is securely fastened presses the child seat from above against the surface of the car seat. Therefore, a downward force toward the car seat increases the seat weight correspondingly. In general, the belt tension is about 10 kgf for a child seat, and 2 kgf for a booster seat, which is almost the same as the case when the seat belt is fastened. The expected seat weights, which are to be increased by the belt tension, are approximately 7 kg and 2 kg respectively. The total weights applied to the car seat are shown in the lower columns (when the seat belt is fastened) of Table 1.
Therefore, as a normal determination, the circumstances of the front passenger seat when the deployment of the air bag should be controlled may be grasped by setting the threshold value of the seat weight to the value between 30 kg and 35 kg. In this case, a known tension switch for detecting the belt tension is used in addition to the seat sensor. The control circuit of the tension switch can maintain the upper and lower threshold values T by setting the same and setting the state of operation as appropriate.
It has been shown that the belt tension of the seat belt used when fixing the child seat onto the car seat differs depending on the configuration of the child seat or the seat body, or on the state of attachment. When the child seat is secured with the seat belt tightly fastened, the belt tension may exceed 10 kg. In this case, the seat weight with an infant sitting thereon may exceed 30 kg. The detected tension may vary by the vibration during driving operation. Therefore, in the method of determination of the state of the passenger as described above, the state of the front passenger seat cannot be determined accurately.
In addition, it may cause a phenomenon similar to the chattering by the vibration associated with the driving operation of the vehicle.
Accordingly, it is an object of the present invention to solve the problems of the related art as described above, and to provide a passenger restraining protective device in which a tension switch is used for determining the state of the passenger sitting on the front passenger seat, and an accurate determination can be made based on seat weight information and information obtained from the tension switch to control whether or not the air bag is to be ignited.
In order to achieve the object described above, the present invention comprises a seat sensor for detecting the load value acting upon the seat, and a tension switch for detecting tension acting on the seat belt and being turned ON when the tension exceeds the threshold value, wherein a control signal for regulating the air bag deployment is supplied when the passenger state is such that the tension exceeds the threshold value and the tension switch is in the ON-state, or that the seat weight obtained from the seat sensor with the switch in the OFF-state is not more than the prescribed weight. Accordingly, the state in which the child seat or the like is fixed on the seat by the seat belt is detected so that the air bag deploying action upon collision is adequately controlled.
In this case, preferably, the tension switch is turned ON when the tension of the seat belt is between 3 kgf and 20 kgf. Accordingly, the air bag deployment is reliably realized when the seat belt is normally used by an adult passenger or the like.
Preferably, the first determined value is obtained by the equation W=xcex1X+Y, where,
W: first evaluation value
xcex1: a conversion factor of the seat load
X: tension load of the tension switch ( less than threshold value)
Y: threshold value of the seat weight,
and the first evaluation value is varied with tension. Accordingly, the errors in weight measurement by the seat sensor or the like caused by tension of the seat belt can be compensated and the accuracy of determination of the state of the passenger by weight measurement can be improved.
Preferably, when the tension switch is in the ON-state and the seat weight is not less than 50 kg, which is set as a second determination value, the regulating control signal is corrected and supplied to execute the deployment of the air bag. Accordingly, malfunction such as a cutoff of air bag for an adult passenger due to failure of the tension switch may be prevented.
Preferably, the regulating control signal is a signal for prohibiting the deployment of the air bag or a signal to decrease the speed of the deployment. Accordingly, the air bag deploying action for a child passenger sitting on the seat is adequately set in advance.
Preferably, the output signal representing the ON-state of the tension switch is effective only when the buckle switch is in the ON-state. Accordingly, non-operation of the air bag due to malfunctioning of the tension switch when the seat belt is not being used is prevented and a diagnosis of failure of the tension switch can be realized.
Preferably, the ON-state of the tension switch is accepted after a prescribed period of holding state. Accordingly, non-operation of the air bag due to chattering of the tension switch caused by the instantaneous change of posture of the passenger can be prevented.